U.S. patent application number 14/518563 was filed with the patent office on 2015-10-22 for mitigating distortion of coated parts during laser drilling.
This patent application is currently assigned to United Technologies Corporation. The applicant listed for this patent is Alan C. Barron, Richard L. Smith. Invention is credited to Alan C. Barron, Richard L. Smith.
Application Number | 20150298261 14/518563 |
Document ID | / |
Family ID | 54321206 |
Filed Date | 2015-10-22 |
United States Patent
Application |
20150298261 |
Kind Code |
A1 |
Smith; Richard L. ; et
al. |
October 22, 2015 |
MITIGATING DISTORTION OF COATED PARTS DURING LASER DRILLING
Abstract
A method for drilling holes in a part includes positioning the
part relative to a laser source, applying a first stress to the
part, and applying a laser from the laser source to the part to
drill a hole therein, wherein the first stress which is present
during the application of the laser counteracts a second stress
induced by the application of the laser.
Inventors: |
Smith; Richard L.; (East
Hartford, CT) ; Barron; Alan C.; (Jupiter,
FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Smith; Richard L.
Barron; Alan C. |
East Hartford
Jupiter |
CT
FL |
US
US |
|
|
Assignee: |
United Technologies
Corporation
Hartford
CT
|
Family ID: |
54321206 |
Appl. No.: |
14/518563 |
Filed: |
October 20, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61893575 |
Oct 21, 2013 |
|
|
|
Current U.S.
Class: |
219/121.71 |
Current CPC
Class: |
B23K 2101/001 20180801;
B23K 2101/34 20180801; B23K 26/0617 20130101; B23K 26/60 20151001;
B23K 26/389 20151001 |
International
Class: |
B23K 26/38 20060101
B23K026/38; B23K 26/02 20060101 B23K026/02; B23K 26/40 20060101
B23K026/40 |
Claims
1. A method for drilling one or more holes in a part, the method
comprising: positioning the part relative to a laser source;
applying a first stress to the part; and applying a laser from the
laser source to the part to drill a hole therein.
2. The method of claim 1, wherein the first stress is present
during the application of the laser, and the first stress
counteracts a second stress induced by the application of the
laser.
3. The method of claim 1, wherein the part includes a first layer
bonded with a second layer.
4. The method of claim 3, wherein the first layer is a metal
substrate and the second layer is a ceramic-based coating.
5. The method of claim 1, wherein the first stress is applied by
pre-bowing the part prior to the application of the laser.
6. The method of claim 1, wherein the first stress is applied by
applying a load to the part while applying the laser.
7. The method of claim 6, wherein the load is varied during the
application.
8. The method of claim 1, wherein the applying the first stress
includes applying heat to the part, wherein the heat is applied on
a side opposite to the side that faces the laser source.
9. The method of claim 8, wherein the heat is generated by laser
drilling performed prior to the application of the laser.
10. The method of claim 8, wherein the heat is generated by laser
drilling performed at approximately the same time as the
application of the laser.
11. A method for drilling one or more holes in a part, the method
comprising: positioning the part relative to a laser source;
pre-bowing the part; and applying a laser from the laser source to
the pre-bowed part to drill a hole therein, wherein the pre-bowing
opposes a stress induced by the application of the laser in the
part.
12. The method of claim 11, wherein the part includes a first layer
bonded with a second layer.
13. The method of claim 12, wherein the first layer is a metal
substrate and the second layer is a ceramic-based coating.
14. The method of claim 11, wherein an amount of the pre-bowing is
predetermined so that the part is not over-stressed.
15. A method for drilling one or more holes in a part, the method
comprising: positioning the part relative to a laser source;
applying a load at the part; and applying a laser from the laser
source to the part to drill a hole therein, wherein the load is
present during the application of the laser and opposes a stress
induced by the application of the laser in the part.
16. The method of claim 15, wherein the part includes a first layer
bonded with a second layer.
17. The method of claim 16, wherein the first layer is a metal
substrate and the second layer is a ceramic-based coating.
18. The method of claim 15, wherein the load is varied during a
period of the application.
19. The method of claim 15, wherein the load is predetermined so
that the part maintains substantially undistorted after the
drilling.
20. A method for drilling one or more holes in a part, the method
comprising: positioning a first side of the part relative to a
laser source; applying heat from a second side of the part, the
second side being opposite to the first side; and applying a laser
from the laser source to the position of the part to drill a hole
therein, wherein the heat is present during the application of the
laser.
21. The method of claim 20, wherein the part includes a first layer
bonded with a second layer.
22. The method of claim 21, wherein the first layer is a metal
substrate and the second layer is a ceramic-based coating.
23. The method of claim 20, wherein the heat is generated by a
laser drilling performed prior to the application of the laser.
24. The method of claim 20, wherein the heat is generated by a
laser drilling performed at approximately the same time as the
application of the laser.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 61/893,575 filed on Oct. 21, 2013 and titled
Mitigating Distortion of Coated Parts During Laser Drilling, the
disclosure of which is hereby incorporated by reference in its
entirety.
BACKGROUND
[0002] The present disclosure relates generally to metallic part
processing, and, more particularly, to a laser drilling process of
metallic parts.
[0003] Laser drilling of cylindrical holes generally occurs through
melting and vaporization of the work piece material through
absorption of energy from a focused laser beam. As a side effect,
laser drilling may cause residual stresses and distortion of
drilled parts. Both the residual stresses and the distortion are
driven by local thermal gradients and their associated gradients in
substrate thermal expansion and transient metallic properties.
Distortion due to laser drilling is often imperceptible but can be
significant in certain structures, in which case a warp will be
formed that may cause failure of the structure, failure of
associated coatings, or result in a final part or structure that
does not satisfy dimensional requirements.
[0004] Accordingly, what is desired is a laser drilling method that
mitigates distortion without significantly impacting production
feasibility and effectiveness.
SUMMARY
[0005] Disclosed and claimed herein is a method for drilling one or
more holes in a part. In one embodiment a method includes
positioning the part relative to a laser source, applying a first
stress to the part, and applying a laser from the laser source to
the part to drill a hole therein, wherein the first stress which is
present during the application of the laser counteracts a second
stress induced by the application of the laser. In one embodiment,
the first stress is introduced by pre-bowing the part prior to the
application of the laser. In one embodiment, the aforementioned
stress is introduced by applying a load at the part while applying
the laser. In one embodiment, the first stress is introduced by
applying heat from an opposite side of the part while applying the
laser.
[0006] Other aspects, features, and techniques will be apparent to
one skilled in the relevant art in view of the following detailed
description of the embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The drawings accompanying and forming part of this
specification are included to depict certain aspects of the present
disclosure. A clearer conception of the present disclosure, and of
the components and operation of systems provided with the present
disclosure, will become more readily apparent by referring to the
exemplary, and therefore non-limiting, embodiments illustrated in
the drawings, wherein like reference numbers (if they occur in more
than one view) designate the same elements. The present disclosure
may be better understood by reference to one or more of these
drawings in combination with the description presented herein. It
should be noted that the features illustrated in the drawings are
not necessarily drawn to scale.
[0008] FIGS. 1A and 1B are cross-sectional views of a coated thin
sheet structure before and after laser drilling according to an
embodiment of the present disclosure.
[0009] FIG. 2 is a diagram illustrating a laser drilling process
according to another embodiment of the present disclosure.
[0010] FIG. 3 is a diagram illustrating a laser drilling process
according to yet another embodiment of the present disclosure.
[0011] FIG. 4 is a flow-chart diagram illustrating a laser drilling
process according to embodiments of the present disclosure.
DESCRIPTION
[0012] One aspect of the disclosure relates to a laser drilling
process. In one embodiment, a method is provided to significantly
reduce laser induced distortion and/or stress in processed parts.
Embodiments of the present disclosure will be described hereinafter
with reference to the attached drawings.
[0013] According to one embodiment of the present disclosure, laser
drilling as discussed herein may be applied to manufacturing of
metallic exhaust liners of aircraft which are coated with
ceramic-based thermal barrier and/or other protective coatings. In
particular, laser drilling of multi-hole film cooling patterns is
used for surface cooling of these liners. One of the advantages of
laser drilling is its ability to drill small and closely space
cylindrical holes at 15-90 degree to the surface with high
efficiency. In multi-hole film cooling, small (0.01-0.2 inch)
closely spaced holes (e.g., from a few to more than 50 holes per
square inch) are used to distribute cooling air and establish a
film.
[0014] FIGS. 1A and 1B are cross-sectional views of a thin sheet
structure 100 before and after a laser drilling process according
to an embodiment of the present disclosure. The thin sheet
structure 100 may be a section of a jet engine exhaust liner.
Referring to FIG. 1A, the thin sheet structure 100 comprises a
metal substrate 102, which is coated with a ceramic-based coating
110 on one side. In addition, a bond coat layer (not shown in FIG.
1A) between the substrate 102 and the coating 110 may be employed
to promote or enhance adhesion of the coating 110 to the substrate
102. In one embodiment, the thin sheet structure 100 is stressed
before undergoing laser drilling, to form a bow shape, or in other
words, is pre-bowed in a manner that will oppose or accommodate a
subsequent laser-induced distortion. As shown in FIG. 1A, a laser
head 112 for drilling is pointed at the coated side 110 of the thin
sheet structure 100, which is convexly bowed toward the laser head
112. The laser head 112 is then activated in a controlled manner to
drill a hole through the thin sheet structure 100. The control can
be in such aspects as energy level, pulsation and duration of the
laser. It is apparent that the laser head 112 can drill either
vertically or at an angle as shown in FIG. 1A.
[0015] Referring to FIG. 1B, a plurality of cooling holes 124
through the thin sheet structure 100 are drilled by the laser head
112. In one embodiment, the thin sheet structure 100 may be bowed
to offset laser-induced distortion, such that the drilled thin
sheet structure 100 returns to its original geometry (flat) after
the laser drilling as shown in FIG. 1B. Here the geometry of the
thin sheet structure 100 refers to a geometric contour of the thin
sheet structure 100 in its elongated direction.
[0016] According to one embodiment, the thin sheet structure may be
bowed to introduce residual tensile stress to the coating 110 which
will aid in accommodating the compressive load induced during laser
processing. Therefore, the pre-bow operation should be performed in
a controlled manner and within the limits of the tensile
capabilities of coating 110, so that the coating durability will
not be compromised. The pre-bow amount can be determined
empirically or through computer simulations for a particular thin
sheet structure.
[0017] FIG. 2 is a diagram illustrating a laser drilling process
according to another embodiment of the present disclosure. A thin
sheet structure 200 remains in its originally flat geometric form,
and comprises the substrate 102 and the coating 110. A laser head
202 is pointed at the coated side 110 of the thin sheet structure
100 for drilling cooling holes. While the drilling is performed, a
load 215 is simultaneously applied on the substrate side 102
pushing the thin sheet structure 100 upward. The load 215 is
designed to offset the thermal load induced by the laser drilling
operation, such that distortion would be minimized. This can be
accomplished through the use of a fixture that can apply the load
215 to the thin sheet structure 100. The load 215 can be varied
throughout the durations of laser drilling and subsequent
cooling.
[0018] Although the original geometric form of the thin sheet
structure 200 is exemplary illustrated as flat, it should be
appreciated that the presently disclosed laser drilling process can
also be applied to other geometric forms. In case of a jet engine
exhaust liner, the original geometric form may be curved.
[0019] In a certain embodiment, an applied load, such as the load
215, would tend to bend the thin sheet structure 100 convexly
toward the coated side 110 to offset the laser-induced load. In
this case, however, an initial elastic preload moment may be
adequate to avoid laser induced distortion. The load 215 and the
initial elastic preload moment may be adequately determined through
empirical optimization trials, potentially supported by
computational modeling on a particular part or assembly.
[0020] FIG. 3 is a diagram illustrating a laser drilling process
according to yet another embodiment of the present disclosure, in
which the goal of mitigating the net and maximum distortion caused
by the laser drilling process is achieved through drilling from
both sides of the thin sheet structure 200 when a circumstance
allows. In one embodiment, a laser head 302 may perform drilling
from the coated side 110, and another laser head 304 performs
drilling from the substrate side 102. In a simple implementation,
approximately one half of the cooling holes (not shown in FIG. 3,
but are similar to the holes 124 in FIG. 1B) would first be drilled
by the laser head 302 and the remaining half of the holes would be
drilled by the laser head 304. The maximum distortion/deflection
encountered with this approach would then be approximately one half
of that encountered with drilling from only one side of the thin
sheet structure 200. In certain embodiments, one quarter of the
holes may be drilled from one side, then another quarter of the
holes from the other side, and so on. In this way, the maximum
distortion encountered may be reduced to approximately twenty five
percent of that encountered with drilling from only one side of the
thin sheet structure 100.
[0021] Although two laser heads 302 and 304 are illustrated in FIG.
3, the thin sheet structure 200 may be rotated after finishing
drilling from one side for drilling from the other side, then only
one laser head is needed. When two laser heads are separately used
on opposite sides, they can be placed close to each other and
simultaneously perform drilling.
[0022] Although each embodiment of the present disclosure are
separately depicted above, it should be appreciated that a
combination of stresses may be applied. For instance, when laser
drilling a first number of holes from a top side of a thin sheet
structure, a load is applied on the bottom side during the laser
drilling. Then flipping over the thin sheet structure for drilling
a second number of holes from the bottom side, this time the same
load can be applied on the top side then.
[0023] It should also be realized that the pre-bowing, the applying
a load and the laser drilling from both sides of a metallic part as
described above all introduce stress in the metallic part, and that
stress is intended to counteract a stress induced by laser
drilling. As a result, distortion of the metallic part may be
avoided after laser drilling according to embodiments of the
present disclosure.
[0024] FIG. 4 is a flow-chart diagram illustrating a laser drilling
process according to embodiments of the present disclosure. The
laser drilling process may be initiated by positioning a metallic
part relative to a laser source in step 402. Next is to apply a
first stress to the metallic part in step 415. Then apply a laser
from the laser source to the metallic part to drill a hole therein
in step 438, wherein the first stress which is present during the
application of the laser counteracts a second stress induced by the
application of the laser.
[0025] It should be apparent that the presently disclosed laser
drilling process is not limited to drilling structures with just
two layers of materials, and the materials are not limited to just
the exemplary metal substrate coated with a ceramic-based coating.
It should be apparent that the presently disclosed laser drilling
process can be applied to any manufacturing process where reduced
distortion of the metallic part is desired.
[0026] While this disclosure has been particularly shown and
described with references to exemplary embodiments thereof, it
shall be understood by those skilled in the art that various
changes in form and details may be made therein without departing
from the spirit of the claimed embodiments.
* * * * *